Current Researches on the Formation of Solidification Microstructure in Alloys
Researches on the theories of microstructure formation in the solidification of alloys are reviewed. Firstly, critical solidification rates from stable to unstable and from unstable to absolutely stable interface according to the perturbation theory are quantitatively expressed. It shows that the microstructure changes from planar interface to cell structure and changes again planar interface. Furthermore, the formation of each microstructure such as planar interface, cell, dendrite and band structure is explained by the phase selection theory. Next, equations on primary dendrite arm spacing, which have been suggested till now, show almost similar form. Finally, transition from columnar dendrite to equiaxed dendrite regions in an ingot is expressed as a function of temperature gradient, which is educed from the interaction of supercooling and nucleation in front of the columnar dendrite.